1. Field of the Invention
The present invention relates to a solid electrolyte fuel cell and a manufacturing method thereof.
2. Description of the Related Art
Fuel cells, as power generators and devices that are clean and can save energy, have been advanced in developing stationary or mobile consumer power sources. Specifically, the fuel cells are attracting attention as household cogeneration power sources and power sources for use in electric cars.
In accordance with the difference of electrolytes, there are various kinds of fuel cells from ones that can be operated in temperatures anywhere from room temperature to ones that can be operated at substantially higher temperatures such as 1000 degrees centigrade; among these, the ones that are now in vigorous development are polymer type fuel cells that can be operated at 100 degrees centigrade or less and have an organic polymer as the electrolyte.
Almost all of the polymer electrolytes that are used in these types of fuel cells are perfluorocarbon sulfonic acid membranes (Trade name: NAFION) developed by E. I. du Pont de Nemours and Company; the membrane exhibits high proton conductivity (from 1×10−2 to 1×10−1 S/cm) in temperatures anywhere from room temperature to 100 degrees centigrade.
Furthermore, in recent years, very small fuel cells called micro-fuel cell are attracting attention as portable power sources in place of secondary batteries. Also, in the electrolyte membranes of this type, NAFION membranes are under study. A fuel cell is a device into which, usually, gaseous fuels such as hydrogen and air are supplied and electricity is extracted. As a fuel for use in mobile and portable fuel cells, an easy-carrying liquid fuel called direct methanol is considered.
At the present time, in the polymer fuel cell that uses the NAFION membrane, since the NAFION membrane has to be maintained in a water-saturated state, water management is necessary.
On the other hand, a solid electrolyte fuel cell, in which the electrolyte is a solid, is free from water; and since an entire fuel cell can be constituted without using a liquid, there are no problems of liquid leakage and liquid replenishment.
However, of the existing solid electrolyte fuel cells with an oxide ion conductor as the electrolyte, there is no report of a phenomenon of the proton conduction at 500 degrees centigrade or less. That is, in order to reduce filim resistance, the protonic oxide conductor has been produced more thinner. However, considering the problem of the mechanical strength of the film, approximately 450 μm is a lower limit; accordingly, in order to obtain sufficient cell output, heating to 500 degrees centigrade or more is considered to be necessary. As a result, there is a problem in that the solid electrolyte fuel cells cannot be used in such applications as cogeneration systems operating at less than 500 degrees centigrade and portable power sources operating in the neighborhood of room temperature.
Furthermore, in a high-temperature operating solid oxide fuel cell that can be operated in the neighborhood of 1000 degrees centigrade, when manufacturing a collective cell, there is a problem in that separators and housing materials, ceramics or heat-resistant alloys that are difficult to manufacture and costly have to be used.
Accordingly, the invention intends to provide a solid electrolyte fuel cell in which a cell output can be obtained even at temperatures lower than 500 degrees centigrade, materials that can be easily machined and are cheaper can be used as a separator and housing material, and a method of manufacturing the same.